The present invention relates to circuit design technology, and more specifically, to a method and apparatus for power delivery network (PDN) analysis.
With the development of integrated circuit techniques, chip integration level has become higher and higher. Digital circuits, analog circuit, RF circuits and other functional circuits are integrated into one single chip, causing increased dynamic current draw (DCD). Thus, simultaneous switching noise (SSN) has become a significant challenge confronted by high speed integration circuit design. SSN has mainly three causing factors: non-ideal signal path inductance, power delivery network (PDN) inductive coupling, and power supply collapse. If SSN exceeds a SSN threshold of an integrated circuit (IC), abnormal operations of functional circuits in the IC may occur as a result.
In general, SSN is measured by noise voltage. According to Ohm's law, SSN caused by PDN is represented as:SSNPDN(jω)=Z(jω)* I(jω)  (1)
Wherein, SSNPDN represents SSN caused by PDN, Z represents PDN impedance, and I represents load DCD. Those skilled in the art may appreciate that in high-frequency circuits, circuits characteristic are all related to frequency, thus SSN, impedance and DCD are represented in the form of complex numbers.
In equation (1), load DCD is related to load characteristics. Given a constant load, the load DCD is also constant. In other words, in the case of a given load, SSN caused by PDN only depends on PDN impedance. In order to make SSN caused by PDN less than the PDN SSN threshold, Z should be less than an impedance threshold. Rather, the amplitude of Z should be less than a certain impedance amplitude threshold. Z of the PDN is determined by its internal structure. Thus, frequency-domain characteristics of the PDN may be determined through designing the internal structure of the PDN, to ensure that the amplitude of impedance Z of the PDN is less than the impedance amplitude threshold. This is known as a frequency-domain analysis method.
The frequency-domain analysis method actually considers steady state characteristics of circuits, without considering transient characteristics in the time domain, because the frequency-domain analysis method only concerns the amplitude of the impedance Z of the PDN, while transient characteristics are reflected by phase. As a solution, PDN simulation can be carried out in the time domain to obtain transient characteristics of the PDN. However, circuit simulation requires consuming a lot of computing resources.
Thus, a new method for PDN analysis is highly desirable.